The first levels in the piano syllabus of Yousician use a notation developed to aid music learning. We introduce the fundamentals of standard notation in a way that teaches the basics. It allows for a smoother transition to the full standard notation later. In these levels, the notation shows the pitch just like in the standard notation, but the rhythmic values are shown using the length of the note bubble.
The note colors recommend which finger to use for playing the single key, e.g. yellow suggests to use the pointer finger.
Check this article to learn more about the different available views and how to change between them.